Mathcad prime 3.1 units problem

[rmaciukiewicz]

Hi, Today i started working in  mathcad prime 3.1 and i have got serious problem with units. Namely i calculate a value and i wanted to add a unit lm/W  -  for example Fi:=.....=145 lm/W and it showed me Fi:= ....= 145 (kg *m^2)/s^3*cd * lm/W but i would like to see only lm/W unit. Is that possible?

[StuartBruff]

Rafał Maciukiewicz wrote:

Hi, Today i started working in  mathcad prime 3.1 and i have got serious problem with units. Namely i calculate a value and i wanted to add a unit lm/W  -  for example Fi:=.....=145 lm/W and it showed me Fi:= ....= 145 (kg *m^2)/s^3*cd * lm/W but i would like to see only lm/W unit. Is that possible?

Yes.

There may be a better way, but this works.

Stuart

[StuartBruff]

StuartBruff wrote:

Rafał Maciukiewicz wrote:

Hi, Today i started working in  mathcad prime 3.1 and i have got serious problem with units. Namely i calculate a value and i wanted to add a unit lm/W  -  for example Fi:=.....=145 lm/W and it showed me Fi:= ....= 145 (kg *m^2)/s^3*cd * lm/W but i would like to see only lm/W unit. Is that possible?

Yes.

evaluate .. delete units ... type in new units

There may be a better way, but this works.

Stuart

In fact, from Help, it looks like that's the official way (I don't generally use units and don't like to clutter my brain with stuff I'll only use once or twice ... like brain cells .. so I generally just do what looks like it might work)

To Convert Units

1. Click to the right of the units to convert. The cursor appears.
2. Press Backspace until all the units disappear. In math regions, the result turns gray.
3. Insert the new units. When you type the units, their names are automatically labeled as units.
4. Press Enter. The units are balanced if needed and the result is recalculated.

Additional Information

• To recover the default units, delete all the units in the unit placeholder and press Enter.
• When you evaluate an array whose elements have incompatible units, the elements are displayed with their own units in base units and you cannot convert these units.

Stuart

[rmaciukiewicz]

It didnt work. Weirde thing is that the unit hasnt change and it looks like that:

[MJG]

In case it's unclear from Stuart's response, note that your equation for fi (the part you've shown as "...") evidently excludes units.  Thus, your result is unitless.  When you tried to add units to the result, it showed your desired units multiplied by the inverse of your desired units.

Instead of adding (or, rather, multiplying by) units in the result, you must do it in the definition/equation.

[StuartBruff]

Mark Gase wrote:

In case it's unclear from Stuart's response, note that your equation for fi (the part you've shown as "...") evidently excludes units.  Thus, your result is unitless.  When you tried to add units to the result, it showed your desired units multiplied by the inverse of your desired units.

Instead of adding (or, rather, multiplying by) units in the result, you must do it in the definition/equation.

Good spot, Mark.  I'd erroneously assumed that was just a typo  ...

Stuart

[rmaciukiewicz]

Ok thx guys for  your help now I've got this. I just need to define all variable with units at first.

[MJG]

Yes.  In your screenshots above, the numbers 45 & 56 need to be multiplied by their appropriate units.  Mathcad then handles unit conversions.

As a more simplified example, you enter the following:

L := 1*m + 20mm = 1.02m

Alternatively, it's often more clear to define more variables:

L1 := 1*m

L2 := 20*mm

L := L1 + L2 = 1.02m

[StuartBruff]

Rafał Maciukiewicz wrote:

Ok thx guys for  your help now I've got this. I just need to define all variable with units at first.

Yes.  And just in case, you don't need to type the "=" after you've done the definition.  fi:=145 lm/W will suffice as in my definition above (I'm confident you knew that, but sometimes the examples can be confusing and lead people into doing things that aren't necessary, so it can be worthwhile pointing it out.  Experienced users (well, at least one) can often fail to see things from a new user's perspective and assume "they know".  On the other hand, there are sufficient differences between how M15 and Prime work that a previous experience may be misleading - which is why I'm now developing the habit of checking everything twice and reading the Help when using Prime!).

Stuart